Altered parietal operculum cortex 2 functional connectivity in benign paroxysmal positional vertigo patients with residual dizziness: A resting‐state fMRI study

Abstract Aims To investigate changes in functional connectivity (FC) focusing on parietal operculum cortex 2 (OP2) in benign paroxysmal positional vertigo (BPPV) patients with residual dizziness (RD) after successful canalith repositioning procedure (CRP). Methods High‐resolution three‐dimensional T1 and resting‐state functional magnetic resonance imaging (fMRI) were performed on 55 healthy controls (HCs), 55 BPPV patients with RD, and 55 patients without RD after successful CRP. Seed‐based (bilateral OP2) FC was calculated to investigate the changes in FC among the three groups. Additionally, we further explored the associations between abnormal FC and clinical symptoms. Results One‐way analysis of covariance showed significant FC differences among the three groups. Post‐hoc analysis showed that patients with RD exhibited decreased FC between left OP2 and regions of left angular gyrus (AG), thalamus, precuneus, middle frontal gyrus (MFG), and right cerebellum posterior lobe (CPL) in comparison with HCs. In addition, compared with patients without RD, patients with RD showed decreased FC between left OP2 and regions of left MFG, AG, middle temporal gyrus, and right CPL. Moreover, in patients with RD, the FC between left thalamus and OP2 was negatively correlated with duration of RD, and the FC between left AG and OP2 was negatively correlated with duration of BPPV. Conclusion BPPV patients with RD showed reduced FC between brain regions involved in vestibular processing and spatial cognition; These results suggested that BPPV patients with RD might have diminished central processing of vestibular information and impaired spatial cognition.


| INTRODUC TI ON
Benign paroxysmal positional vertigo (BPPV) is the most common peripheral vertigo disease. 1 Epidemiology showed that the lifetime prevalence of BPPV was 2.4%, the annual prevalence was 1.6%, and the annual incidence was 0.6%. 2 Canalith repositioning procedure (CRP) is the most important treatment for BPPV, which removes the otolith from the affected semicircular canal and gets rid of vertigo instantly upon most occasions. 3However, 31% to 61% of BPPV patients still suffer from residual dizziness (RD) lasting a few weeks to several months after successful CRP.These BPPV patients with RD usually complain of a non-specific dizziness, imbalance, or unsteadiness, without positional vertigo and nystagmus. 4,5rrently, the potential neural mechanism of RD remains unclear.Some studies considered that the occurrence of RD was attributed to incomplete central nervous system adaptation and compensatory. 6,7recent resting-state functional magnetic resonance imaging (fMRI) study suggested that patients with BPPV exhibited increased fractional amplitude of low-frequency fluctuations (fALFF) in region of pons, functional changes in pons might reflect central adaptation and compensatory after repeated attacks of episodic vertigo.8 Previous studies have also shown that the vestibular nucleus of the pons might play an important role in central compensation in patients with unilateral external vestibular damage or in rats model of acute unilateral labyrinthotomy.9,10 In central vestibular pathway, it was confirmed that the vestibular nucleus relies on vestibular information to the vestibular cortex through the thalamus.11 It was reported that the parieto-insular vestibular cortex (PIVC) was the core of the human vestibular cortex, and parietal operculum cortex 2 (OP2) was the core of PIVC and was considered to be the primary vestibular cortical region in humans.12,13 Thus, it is reasonable to think that the vestibular nucleus relies on vestibular information to the OP2 through the thalamus, and the functional changes in pons (vestibular nucleus) in patients with BPPV may indicate abnormal functional activity of the OP2.However, it is currently not clear whether BPPV patients with RD showed abnormal functional activity of the OP2.
Therefore, the present study aimed to evaluate the alterations in resting-state functional connectivity (FC) focused on the bilateral OP2 and to determine whether these changes in FC correlate with certain clinical features in BPPV patients with RD after successful CRP.We hypothesize that the neural mechanism of RD involves functional changes in brain pathways through the OP2, and the altered FC of OP2 may potentially become an imaging biomarker for the diagnosis of RD in patients with BPPV.

| Participants
Between March 2020 and June 2023, 165 right-handed subjects were recruited at the Second Affiliated Hospital of Xuzhou Medical University, including 55 BPPV patients with RD, 55 BPPV patients without RD, and 55 healthy volunteers.The BPPV patients were diagnosed using the criterion established by Bárány Society in 2015. 14ior to enrollment, all patients underwent routine neuro-otological interrogations and examinations to exclude secondary BPPV resulting from vestibular neuritis (VN), Meniere's disease (MD), vestibular migraine (VM), or head trauma.Patients with central nervous system disorders, psychiatric, or systemic disorders were excluded.
BPPV with superior semicircular canal (SSC) or multi-canal (MC) are rare.It was reported that SSC-BPPV accounts for 1% to 3% of cases and the MC-BPPV accounted for no more than 5% of patients with BPPV. 15,16In addition, according to a recent systematic review and meta-analysis, the affected side, location, or type of semicircular canal involvement have no concern with the occurrence of RD. 17 Therefore, we only included BPPV patients with unilateral posterior semicircular canal (PSC) or horizontal semicircular canal (HSC); patients with MC or SSC were excluded.
Once diagnosed, patients with PSC-BPPV were treated with Epley's maneuver 18 or Semont maneuver 19,20 and patients with HSC-BPPV were treated by Barbecue rotation maneuver (geotropic lateral canal BPPV) 21 or Gufoni maneuver (apogeotropic lateral canal BPPV). 22,23A Dix-Hallpike or supine-roll test was performed 1 h after CRP to ensure a successful treatment. 24,25After a successful CRP, the following demographic and clinical data were collected, including age, sex, educational years, affected side, involved semicircular canal, and duration of BPPV before successful CRP.In addition, scores of dizziness handicap inventory (DHI) and vertigo visual analog scale (VVAS) before successful CRM were collected.
Then, all patients experienced 1 week follow-up evaluation through interviews.During the interviews, the identification of RD symptoms was performed.Scores of DHI and dizziness VAS (DVAS) for patients with RD after successful CRP were recorded.All patients with and without RD underwent resting-state fMRI scanning.In addition, the duration of RD symptoms for each patient with RD was collected.As symptoms of BPPV or RD may lead to anxiety and depression, some patients may even transition to persistent postural perceptual dizziness (PPPD, a chronic functional vestibular disorder which is characterized by persistent non-rotational dizziness and instability combined with anxiety and depression lasting more than 3 months). 26  Our study was approved by the Ethics Committee of the Second Affiliated Hospital of Xuzhou Medical University ( 【2020】021801) and all subjects provided written informed consent forms before entering the study.

| Imaging acquisition
All Participants received high-resolution three-dimensional T1weighted (3D-T1) anatomical imaging and resting-state fMRI using a

| Image data preprocessing
To reduce the influence of initial unstable blood-oxygenation-level-

| Seed-based functional connectivity
After preprocessing, filtering (0.01-0.08 Hz) was adopted to eliminate the influences of low-frequency drift and high-frequency noise.
Cerebrospinal fluid, white matter, and global mean signals, as well as the 24 motion realignment parameters were regressed out.We performed a seed-to-voxel method using two seeds (the bilateral OP2) related to key vestibular cortex of the brain.We extracted the two seeds from the Juelich histological atlas available on the FMRIB Software Library (https:// fsl.fmrib.ox.ac.uk/ fsl/ fslwi ki/ Atlases).
Then, the mean time-courses of the two seeds were extracted and the Pearson's correlation coefficients (r) between the extracted time-courses and all other time-courses of the entire brain voxels were calculated.Finally, r was converted to z scores using Fisher's rto-z transformation.It is now still complex and controversial whether to remove the global mean signal.Therefore, we also performed an analysis without using global signal regression (GSR) and the results are demonstrated in Tables S1 and S2 and Figures S1-S3.

| Analysis of demography and clinical characteristics
Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS, v22.0) for Windows (SPSS Institute Inc.).
All data of continuous variables were tested for normality.Group comparisons of demographic information among the three groups were performed using chi-square tests for categorical variables (gender) and one-way analysis of covariance (ANOVA) for parametric continuous variables (age, years of education, scores of MoCA, HAMA, and HAMD).For BPPV patients with and without RD, the two-sample t-tests were used for parametric continuous variables (scores of VVAS and DHI, and duration of vertigo before successful CRM) and chi-square tests were used for categorical variables (affected side and affected semicircular canal).

| Analysis of differences in FC
Group differences in FC among the three groups were tested using a voxel-wise one-way ANOVA, with age, gender, years of education, scores of MoCA, HAMA, and HAMD as covariates.To show the inter-group differences, we performed post-hoc two-sample t-tests between every two of the three groups, controlling for demographic and clinical features severally.The post-hoc inter-group comparisons were performed within the mask which showed FC differences from the ANOVA analysis.Multiple comparisons were corrected by a false discovery rate (FDR) method (p < 0.05).

| Demographic and clinical characteristics
The demographic and clinical characteristics of the three groups were summarized in Table 1.As we could see, there was no statistical difference among the three groups in age, gender, education level, scores of MoCA, HAMA, and HAMD (all p > 0.05).In addition, no significant difference was observed between BPPV patients with and without RD in affected side, affected semicircular canal, and VVAS scores before successful CRP (all p > 0.05).However, BPPV patients with RD showed longer duration of BPPV (p = 0.002) and higher DHI scores (p = 0.005) before successful CRP in comparison with BPPV patients without RD.

| FC differences across groups
When the left OP2 was selected as a seed, the three groups showed significant FC differences in the left angular gyrus (AG), left middle frontal gyrus (MFG), superior frontal gyrus (SFG), parahippocampa gyrus, and middle temporal gyrus (MTG), as well as the bilateral thalamus, precuneus, and cerebellar regions (p < 0.05, FDR corrected; Figure 1).When the right OP2 was chosen as a seed, one-way ANOVA revealed no obvious difference among the three groups in FC.The post-hoc results demonstrated that BPPV patients with RD exhibited decreased FC between the left OP2 and regions of the left AG, thalamus, precuneus, MFG, and the right cerebellum posterior lobe (CPL) in comparison with healthy subjects (p < 0.05, FDR corrected; Figure 2, Table 2); Beyond that, compared with BPPV patients without RD, patients with RD showed decreased FC between the left OP2 and regions of the left MFG, AG, MTG, and the right CPL (p < 0.05, FDR corrected; Figure 3, Table 3).
In results without GSR, the FC patterns of the OP2 with other brain regions were similar to the above results with GSR.The difference in results without GSR was that the left OP2 showed decreased FC with left fusiform gyrus in BPPV patients with RD compared with healthy controls, and the left OP2 displayed decreased FC with right superior parietal lobule and left inferior parietal lobule in BPPV patients with RD compared with patients without RD (p < 0.05, FDR corrected; Tables S1 and S2 and Figures S2 and S3).

| Associations between FC and clinical characteristics in BPPV patients with RD
As shown in Figure 4, in BPPV patients with RD, the FC (z-value) between left thalamus and OP2 was negatively correlated with the duration of RD symptoms (p = 0.025, r = −0.313),and the FC (z-value) between left AG and OP2 was negatively correlated with the duration of BPPV (p = 0.011, r = −0.352).

RD (n = 51)
Without  Compared with patients without RD and healthy subjects, patients with RD exhibited decreased FC between left OP2 and left AG.
The AG is located in a posterior part of the inferior parietal lobule corresponding to Brodmann Area (BA) 39. 27 A functional neuroimaging study suggested that the bilateral AG were significantly activated during task of spatial navigation. 28It was also reported that there existed structural plasticity in the AG when subjects were learning new skills that tap on spatial coordination. 29Thus, it is believed that the AG is involved in spatial which reflects our ability to process and integrate all spatial aspects of our environment, including the spatial analysis of external sensory information and internal mental representations. 30The functional changes in the left AG have been previously observed in patients with chronic unilateral vestibulopathy during rest and in patients with PPPD during stationary emotional stimulation. 31,32Our study found altered function in AG in BPPV patients with RD, which was consistent with a previous F I G U R E 1 Brain regions showing significant FC differences among the three groups when the left OP2 was selected as a seed (one-way ANOVA, p < 0.05 (FDR corrected)).ANOVA, Analysis of covariance; FC, Functional connectivity; FDR, False discovery rate; L, Left; OP2, parietal operculum cortex 2; R, Right.
resting-state fMRI study which reported decreased ALFF in the AG in BPPV patients with RD compared to patients without RD. 33We also found that the FC between left AG and OP2 was negatively correlated with the duration of BPPV.Our results indicated impaired spatial cognition in BPPV patients with RD, and the occurrence of RD might be related to the reduced FC between the areas involved in central vestibular processing and spatial cognition.
We also found decreased FC between the left OP2 and right CPL/Crus2 in BPPV patients with RD compared to patients without RD and healthy controls.Central vestibular pathway involves the cerebellum, as the projections from the vestibular nuclei extend to the cerebellum. 34The cerebellum is an important area playing a vital role in maintaining balance and coordination of the goaloriented movements. 35The cerebellum is closely associated with dizziness and vertigo; stroke with lesions within the cerebellum is one of the most common causes of vascular vertigo. 36As part of the cerebellum, the CPL/Crus2 was reported to be closely related to spatial cognition, playing an important role in spatial navigation and orientation. 37,38The altered function in CPL/Crus2 found in our study was in keeping with the abnormal gray matter volume (GMV) and regional homogeneity (ReHo) in CPL/Crus2 in patients with BPPV in a previous neuroimaging study. 8Thus, we suspected that the decreased FC between left OP2 and right CPL/Crus2 might also indicate reduced connectivity between the regions engaged in vestibular processing and spatial cognition.
The MFG was previously thought to be involved in vestibular processing and was reported to be a part of vestibular network, as it was obviously activated during tasks of vestibular or caloric stimulation. 39,40The MFG receives vestibular information from vestibular nuclei and is believed to be the origin of direct white matter fibers to the vestibular nuclei. 413][44][45][46] In BPPV patients with RD, we found decreased FC between left OP2 and left MFG when comparing to BPPV patients without RD and healthy controls.The decreased FC between OP2 and MFG in our study might suggest decreased connectivity within the central vestibular network.
F I G U R E 2 Differences in FC between BPPV patients with residual dizziness (RD) and healthy controls (HC) when the left OP2 was chosen as a seed (two-sample t test, p < 0.05 (FDR corrected)).AG, Angular gyrus; BPPV, Benign paroxysmal positional vertigo; CPL, Cerebellum posterior lobe; FC, Functional connectivity; FDR, False discovery rate; L, Left; MFG, Middle frontal gyrus; OP2, parietal operculum cortex 2; R, Right.8][49] In this study, we found decreased FC between left OP2 and left thalamus in BPPV patients with RD, indicating decreased thalamo-OP2 vestibular pathway.In addition, we observed that the FC between left thalamus and OP2 was negatively correlated with duration of RD.As all fMRI data were collected at the early stage of RD symptoms (within 1 week), we believed that the decreased FC between left thalamus and OP2 potentially predict the development and the duration of residual dizziness in patients with BPPV.
The precuneus is a core region of default mode network (DMN) and plays a crucial role in attention monitoring and self-centered cognition. 50It was demonstrated that electrical stimulation of the precuneus evoked symptom of vertigo, suggesting that the precuneus was an important brain region in processing vestibular information. 51,52In the present study, we observed decreased FC between left OP2 and left precuneus in BPPV patients with RD compared to healthy controls; this result was in agreement with a previous resting-state fMRI study which reported decreased ALFF in the bilateral precuneus in BPPV patients with RD. 33 Our results of decreased FC between left OP2 and left precuneus in BPPV patients with RD might indicate decreased connectivity within the vestibular network.

| Limitations
This study has certain limitations in some aspects.First, the sample size of the present study was relatively small and only resting-state fMRI was adopted, a multi-model MRI study with larger sample size should be considered in the following study.Second, we only This might have some influence on the conclusion of this study.

| CON CLUS IONS
In summary, the current study found that BPPV patients with RD showed reduced FC between brain regions involved in vestibular pro-

ACK N OWLED G M ENTS
We thank all the subjects for their participation in this study.

FU N D I N G I N FO R M ATI O N
This study was funded by Xuzhou Municipal Health Commission (No. XWKYHT20200010) and Health Commission of JiangSu province (H2023014).

CO N FLI C T O F I NTER E S T S TATEM ENT
All the authors declare that they have no conflict of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings will be available in China Clinical All patients were assessed by Hamilton Anxiety Scale (HAMA) and Hamilton Depression Scale (HAMD) during the follow-up; patients with scores of HAMA > 14 or HAMD > 17 were excluded.Patients with RD symptoms lasting more than 3 months were excluded.Fifty-five age-, gender-and education-matched volunteers were recruited.They had no history of vertigo, nor did they have a history of drug or alcohol abuse.Volunteers with neurological, mental, or systemic disorders were excluded.They received resting-state fMRI scanning and demographic information was gathered.To rule out the effects of cognitive impairment on the brain function of the subjects, all subjects were evaluated by Montreal Cognitive Assessment (MoCA); participants with scores of MoCA < 26 were excluded.Assessments of MoCA, HAMA, and HAMD were conducted by a qualified neuropsychologist who was blinded to the outcome data.
dependent (BOLD) signal, the first 10 functional time points were removed; the left 200 time points were preprocessed using Statistical Parametric Mapping 12 software (SPM12, http:// www.fl.ion.ucl.ac.uk/ spm/ softw are/ spm12 ) and CONN toolbox (Whitfeld-Gabrieli S, 2012; Version 18b; http:// www.nitrc.org/ proje cts/ conn) working on MATLAB R2016a (MathWorks, Inc.).The preprocessing steps were the default parameters within the CONN toolbox, including (a) functional slice-timing correction, (b) functional realignment, (c) functional outlier detection (a subject head motion threshold set at 3 mm and a global signal threshold set at z = 9), (d) structural center to (0, 0, 0) coordinates (translation), (e) functional segmentation and normalization (DARTEL), and (f) spatial smoothing based on a Gaussian kernel of 6-mm full-width at half maximum.Four patients in RD group, five patients in non-RD group, and two healthy subjects were excluded due to large head motion or poor normalization.Totally, 51 patients with RD, 50 patients without RD, and 53 healthy subjects were included in the following analysis.

For
FC showing significant between-group differences, we performed Pearson's partial correlation analysis between altered FC and clinical characteristics (duration of vertigo, scores of VVAS and DHI before successful CRM, and duration of RD, scores of DVAS and DHI after successful CRM) in BPPV patients with RD, controlling for age, gender, educational years, MoCA, HAMA, HAMD, affected side, and affected semicircular canal.The significance level was set at p < 0.05.

TA B L E 1
Demographic and clinical characteristics of the subjects.This study is the first one which investigated resting-state FC changes focusing on OP2 in BPPV patients with RD after successful treatment.The results showed altered FC between the left OP2 and regions of the left AG, MFG, thalamus, precuneus, MTG, and the right CPL in BPPV patients with RD compared to BPPV patients without RD and healthy volunteers.
cessing and spatial cognition.These results suggested that BPPV patients with RD might have diminished central processing of vestibular information and impaired spatial cognition.In addition, the reduced FC could potentially become an imaging biomarker for the early diagnosis of RD in patients with BPPV, which should be further verified by machine learning (ML) methods with more subjects in the future.AUTH O R CO NTR I B UTI O N SZhengwei Chen and Yueji Liu designed the study, analyzed the data, and wrote the main manuscript; Cunxin Lin, Dan Liu, and Lijie Xiao collected the data; Haiyan Liu and Xiu-e Wei organized the data; Liangqun Rong revised the manuscript.All authors contributed to the article and approved the submitted version.

F
I G U R E 4 (A) Functional connectivity (FC) between the left thalamus and the left parietal operculum cortex 2 (OP2) was negatively correlated with the duration of residual dizziness (RD) (p = 0.025, r = −0.313);(B) FC between the left angular gyrus (AG) and the left OP2 was negatively correlated with the duration of benign paroxysmal positional vertigo (BPPV) in patients with RD (p = 0.011, r = −0.352).

Brain regions Voxel size Peak MNI coordinates x, y, z
Altered FC of the left OP2 in BPPV patients with RD compared with healthy controls.